OBJECTIVE: To investigate the prevalence of obesity and its association with socioeconomic factors and comorbidities in a population-based study. MATERIAL AND METHODS: Data were examined from 4 605 persons ages 60 and older that participated in the 2001 Mexican Health and Aging Study, conducted in rural and urban communities in Mexico. The prevalence of obesity (according to self-reported weight and height) was obtained, stratified by age, and logistic regression was used to study cross-sectional associations between obesity and socioeconomic factors. RESULTS: Of the population studied, 20.9% were classified as obese and the prevalence diminishes with age. Overall, women were more likely than mentobe obese. Lower educational level was associated with lower risk of overweight. In both men and women, obesity was more common between subjects with hypertension (OR 1.38 and 1.71, respectively) and long-distance walk limitation (OR 2.08 and 2.21, respectively). CONCLUISON: In older Mexican adults, hypertension and long-distance walk limitation were independent associated factors for higher prevalence of obesity.

Obesity is a serious public health problem that is becoming very common in developed and developing countries. Agreat number of persons become overweight or obese as they get older, which is associated with a decrease in physical activity and basal metabolism, and a body fat redistribution to the abdominal area.1

Several studies have found that the association between obesity and mortality is lower in elderly persons; however, morbidity increases with body mass index.2,3 Overweight and obesity are associated with medical conditions such as hypertension, type 2 diabetes mellitus, osteoarthritis, respiratory disease,4,5 and depression.6,7 They are also related with diminished functional status, principally because of mobility limitations. Decrease in physical activity causes de-conditioning and the risk of fragility.8

The association between obesity and cardiovascular disease has been reported in the adult population; however, there are few studies of elderly patients and the results are contradictory.9

In several surveys, tobacco and alcohol consumption have been found to be factors associated with a lower prevalence of obesity and overweight, mainly because of a decrease in intake and an increase in energy expenditure.10

According to the National Center for Health Statistics, in 2000 the obesity rate for the U.S. population ages 65-74 years was 36.05%.11 In 1997, in Canada the prevalence of overweight and obesity in people ages 65 and older were 43.3 and 20.9%, respectively.12

In developing countries where overnutrition and undernutrition co-exist, the figures are also important. In Mexico, the 2000 National Health Survey showed that the prevalence of obesity and overweight increased from 21.5% in 1993 to 23.7% in 2000. In people ages 60-79 years, 39% were overweight and 26% were obese. 13

Several studies in both developed and developing countries show that in all age groups, overweight is more prevalent in men and obesity is more prevalent in women. An increase in overweight and obesity according to age can be observed, however between 60 and 65 years of age, the body mass index (BMI) began to decrease.14,15

Information about distribution of obesity betweensocial classes in older populations is poor and results obtained in young and adult populations are contradictory. Several studies have confirmed an inverse association between obesity and socioeconomic levelin adult women in developed countries; however, this association has not been observed in men and children. Studies in developing countries have foundgreater occurrences of obesity in higher socioeconomic classes.16

Few studies have evaluated overweight and obesity prevalence and its determinants, or their relation with morbidity and mortality in the elderly Latin American population. The aim of this study was to investigate the prevalence of obesity and its independent associations with socioeconomic factors and comorbidities such as hypertension, myocardial infarction and diabetes in a large population-based study.

Material and Methods

The 2001 Mexican Health and Aging Study (MHAS) database was analyzed.17 The MHAS is a cross-sectional, population-based study conducted in rural and urban communities in Mexico in 2001. Data from 7 170 persons older than 60 years of age were included. From this, 4 905 had self-reported weight and height which were verified by Avila-Funes (2004), who concluded that it is a valid method that can be used to accurately estimate height and weight in elderly Mexican people.18 Informed consent was obtained for all subjects according to the "Declaration of Helsinki on Ethical Principles for Medical Research Involving Human Subjects".

Based on self-reported weight and height, body mass index (BMI) was calculated by dividing total body weight (kilograms) by the squared standing height (square meter). Using this index, patients were grouped, according to the World Health Organization classification,19 into low body weight (BMI<19.9), normal body weight (BMI 20 to 24.9), overweight (BMI 25 to 29.9) and obesity (BMI> 30). From this analysis we excluded 300 (6.1%) patients with low body weight (BMI<19.9).

Results are presented as percentages. For the proportion comparison among variables, Pearson x2 was used. Using stepwise logistic regression analyses, predictors of overweight and obesity relative to normal weight were examined. Analyses were stratified by gender. A p value< 0.05 was considered significant. The SPSS Inc. (Version 10.0) statistical program was used for the statistical analysis.

Results

Out of 4 605 persons studied, 2 392 (51.9%) were men and2 213 (48.1%) were women. Normal weight was presentin 35.8%, overweight in 43.3%, and obesity in 20.9% of thetotal population studied. Figure 1 shows the distributionof normal weight, overweight and obesity among menand women stratified by age and gender. Women weremore likely to be obese compared to men (24.8 vs. 17.3%).In both men and women, prevalence of overweight andobesity were low in the oldest age groups.

All socioeconomic and health variables included in this study have significant differences when compared by gender, with the exception of age, education level, respiratory disease, stroke and current smokers.

Table I shows demographic and socioeconomic characteristics stratified by gender in subjects with normal weight, overweight and obesity. There is a statistically significant lower occurrence of single men classified as overweight and obese compared with normal weight. People with a low educational level have a lower prevalence of overweight. In subjects classified as overweight, there were fewer men who self-rated their socioeconomic status as poor.

Table II shows health characteristics stratified bygender in subjects with normal weight, overweight andobesity. In women, a self-rated health status of poorand arthritis were associated with obesity. Hypertension, diabetes mellitus, comorbidity, and long-distancewalk limitation were more frequent in subjects classified as obese compared with normal. In men, therewas a higher occurrence of myocardial infarction anda lower occurrence of bowel disease associated with overweight. Current smokers had a statistically significant lower prevalence of obesity and overweightin both genders. Alcohol consumption was associated with risk of overweight.

Results from logistic regression analysis, with adjusted odds ratio for the relationship between studied variables and overweight or obesity, are presented in Table III. Overall, women were more likely than men to be obese (OR 1.47). Lower educational level was significantly associated with lower risk of overweight (among men andwomen, OR 0.80 and 0.67, respectively). Among men, poor economic self-perception and bowel disease were inversely associated with overweight and obesity, respectively. In the total population, obesity was associated witha higher risk of myocardial infarction (OR 1.61), but inthe analysis stratified by gender there was no significant association. In both men and women, obesity was more common between subjects with hypertension (OR 1.38and 1.71, respectively) and long-distance walk limitation (physically inactive) (OR 2.08 and 2.21, respectively). Ageand tobacco use were inversely associated with obesity inmen (OR 0.50 and 0.61, respectively) and with overweightin women (OR 0.76 and 0.66, respectively). The other variables were not significantly associated with the riskof overweight or obesity.

Conclusion

The prevalence of obesity and overweight according to age and gender found in the present study was similar to that which was found in the Mexican National Health Survey, in which the occurrence of obesity starts to decline from the 60 to 69 years age group to the age group 80 years and older, probably caused by population surveillance. In men 60 to 69 years old, obesity was found in 24.4% of the men, in the 70 to 79 years age group it was 16.5%, and in the age group 80 years and older, 10.7%. In comparison, in women ages 60 to 69 obesity was 36.5%, in the 70 to 79 years age group it was 27.9%, and in the age group 80 years and older, 17.3%. 13

In this study, it was found that a lower educational level was associated with a lower prevalence of overweight in women and men, and a poor self-rated socioeconomic status in men. This is in concordance with Stunkard,16 who stated that in developing countries, people from lower educational levels and with a lower socioeconomic status may have difficulties getting accessto sufficient food in order to become fat. On the other hand, in developed countries, people with a lower socioeconomic status have a higher prevalence of overweightand obesity because they have access to food but less knowledge about nutrition and poor physical activity.

It is important to take into account the great differences that exist in the health and nutrition of the Mexican population. People who live in cities generally present similar characteristics to those in developed countries (a greater prevalence of obesity and a tendency to besedentary), and those living in rural areas tend to be thinner, their alimentation is mainly based on grains and vegetables and they have greater physical activity.

On the other hand, in the present study, the economic situation was defined based on self-perception and not on investigating the actual situation based on a set of socioeconomic variables. Therefore, the comprehensive investigation of the relation between socioeconomic conditions and obesity is considered to be important.

Hypertension and long-distance walk limitation were independently associated with obesity in men and women. These results are consistent with several studies that show that high BMI (past or current) is associated with a greater risk of self-reported functional limitation (especially mobility) among older persons. Subjects with a BMI ranking between 23 and 27 had about three times less chance of being ADL dependent in five years.20 Risk of loss of mobility is significantly associated with high BMI (>80th percentile) compared with moderate (21st-80th percentiles) BMI.21 Several studies have also shown that BMI and fat mass are positively related to disability, limitation in activities of daily living, walking upstairs, walking on flat surfaces, pulmonary disease, diabetes, and arthritis.22

In men, we found that smoking was inversely related to obesity, which is in accordance with Garrison et al. 1983 who state that smoking is clearly related to body size: lean individuals are more likely to be smokers than are those of normal or excess weight.23 Cigarette smoking appears to reduce body fat in a number of ways, including a reduction in caloric intake and an increased level of energy expenditure. Smoking cessation is also related to body size. Studies of mortality generally found that current smokers are leaner and have higher mortality than nonsmokers or past smokers.

Diabetes and arthritis-two diseases most commonly associated with excess weight-were not significantly associated with overweight or obesity. These results could be explained because subjects who are prone to the complications of overweight and obesity may have already died, leaving those who are more resistant to its effects.24

In this study, we found an effect of obesity on myocardial infarction in the total population, but this effect disappears in the gender-stratified analysis. The evidence of the effect of overweight and obesity in the incidence of cardiovascular disease is contradictory in some cases or not consistent in the literature.25

Data from weight and height were obtained fromself-reports and could be underestimated or overestimated, especially in people 75 years and older; in the literature, however, we found that several studies have consistent findings of high correlations of self-reported height and weight with measured height and weight.26

Another aspect to consider about self-reporting is that people with a low educational level and or with cognitive decline would be underestimated.

In conclusion, some evidence was found of an association between overweight and obesity and some common health and sociodemographic conditions in the elderly; however, it is important to conduct longitudinal studies in order to discover the effect of BMI and other nutritional status indicators, such as body composition, on this population health group. This information can be useful for nutritionists and physicians who work with elderly people, in terms of making decisions as to whether or not to recommend losing weight.

5. National Institutes of Health, National Heart, Lung, and Blood Institute; NHLBI Obesity Education Initiative; and North American Association for the Study of Obesity. Identifying, evaluating, and treatment overweight in adults. Pan Am J Public Health 2001;10(2):118-125. [ Links ]